1. Field of the Invention
The present invention relates to an improved waterproof and breathable sole for shoes and to the shoe manufactured with such sole.
2. Description of the Related Art
Waterproof and breathable soles made of plastics for shoes are already known.
One of such soles is disclosed in WO 97/14326.
In this case, the sole comprises:                a mid-sole with a membrane made of a material that is impermeable to water and permeable to water vapor, associated with a lower protective layer of a material that is resistant to hydrolysis, water-repellent, breathable and/or perforated;        a tread made of perforated elastomer, which is joined perimetrically and hermetically to the mid-sole.        
The waterproof and breathable sole disclosed in WO 98/51177 is also known; it comprises a preassembled insert in which there is a membrane that is impermeable to water and permeable to water vapor, associated with a lower protective layer made of a material that is resistant to hydrolysis, water-repellent, breathable and/or perforated.
The insert is completed by an element that is overmolded or over-assembled, surrounds the membrane and the protective layer, and is joined hermetically to them.
The insert is part of a mid-sole and is joined, together with said mid-sole, to a tread made of perforated plastic material, which is overmolded or over-assembled.
In both cases, the protective layer arranged below the membrane is designed to protect it against piercing due to foreign objects that have accidentally passed through the holes.
The protective layer is usually made of felt and is coupled to the membrane in a breathable manner (by means of spots of thermoplastic adhesive, for example of the polyurethane-based type) to allow the passage of the vapor from the inside of the shoe toward the outside through the holes provided in the tread.
Breathable and waterproof soles for shoes are also known from U.S. Ser. No. 09/978,634 and EPA No. 01124210.4 and comprise, at least along part of their extension, a lower waterproof component that constitutes the tread, an upper component with a supporting structure that is provided with holes connected to outlets at least on the upper and edge surfaces, and a waterproof vapor-permeable membrane that surrounds externally at least the outward-facing regions of the upper component.
The lower component, the upper component and the membrane are joined hermetically in the regions of possible internal water infiltration.
Although the above described soles have now been available commercially for years and are unanimously acknowledged as being capable of producing an exchange of heat and water vapor between the microclimate inside the shoe and the external microclimate, such soles, in some cases, such as for example use on the part of users with quantitatively higher-than-average foot perspiration, have been found to have a breathability that is insufficient to fully dispose of the generated vapor and ensure the correct microclimate inside the shoe.
The structure of the above described soles in fact has, at least in a downward region, layers of microperforated plastic material, i.e., provided with holes having a diameter on the order of 1-2 millimeters, and the total area of the microperforations in any case limits the area of the membrane that is actually affected by the exchange of heat and vapor.